Performance of a microwave radiation induced persulfate-hydrogen peroxide binary-oxidant process in treating dinitrodiazophenol wastewater

Abstract

A persulfate-hydrogen peroxide (PS-H2O2) binary-oxidant system activated by microwave (MW) radiation was used to treat dinitrodiazophenol (DDNP) industrial wastewater. While evaluating the treatment efficacy of the MW-PS-H2O2 process, the effects of MW power, PS dosage, n(PS)/n(H2O2) ratio, and initial pH on chemical oxygen demand (COD) removal and reaction kinetics (kobs) were investigated. The transformation of organics was also examined. The best treatment efficacy (COD removal = 73.92% and kobs = 0.1996 mg/(L min)) after a reaction time of 16 min was achieved using optimized operation parameters (initial pH = 3.0, PS dosage = 3.70 mmol/L, H2O2 dosage = 2.45 mmol/L, MW power = 450 W). Increasing MW power and PS dosage within certain ranges and an acidic environment improved treatment efficacy, but too high MW power and too low H2O2 dosage (indicated by too high n(PS)/n(H2O2) ratio) significantly inhibited treatment efficacy. The benzene-ring structure, nitro group, and diazo group of organics in the wastewater were greatly degraded. The radicals SO4·- and ⋅OH were major contributors to organics degradation, and the major reactive oxygen species differed under different operation parameters. The MW-PS-H2O2 process improved the biodegradability of the wastewater 10-fold (to 0.606) and required approximately half as much electrical power as comparative processes (MW-PS and MW-H2O2). Therefore, the MW-PS-H2O2 binary-oxidant process is an effective and promising DDNP industrial wastewater pre-treatment method, and shows superior treatment efficacy compared to single-oxidant processes while also consuming less electrical power.